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      7.5.&nbsp;General Network Configuration
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        Linux From Scratch - Version 8.0
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      <h3>
        Chapter&nbsp;7.&nbsp;System Configuration
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    <div class="sect1" lang="en" xml:lang="en">
      <h1 class="sect1">
        <a id="ch-scripts-network" name="ch-scripts-network"></a>7.5. General
        Network Configuration
      </h1>
      <p>
        This section only applies if a network card is to be configured.
      </p>
      <p>
        If a network card will not be used, there is likely no need to create
        any configuration files relating to network cards. If that is the
        case, you will need to remove the <code class=
        "filename">network</code> symlinks from all run-level directories
        (<code class="filename">/etc/rc.d/rc*.d</code>) after the bootscripts
        are installed in <a class="xref" href="bootscripts.html" title=
        "7.2.&nbsp;LFS-Bootscripts-20150222">Section&nbsp;7.2,
        &ldquo;LFS-Bootscripts-20150222&rdquo;</a>.
      </p>
      <div class="sect2" lang="en" xml:lang="en">
        <h2 class="sect2">
          7.5.1. Creating Network Interface Configuration Files
        </h2>
        <p>
          Which interfaces are brought up and down by the network script
          usually depends on the files in <code class=
          "filename">/etc/sysconfig/</code>. This directory should contain a
          file for each interface to be configured, such as <code class=
          "filename">ifconfig.xyz</code>, where <span class=
          "quote">&ldquo;<span class="quote">xyz</span>&rdquo;</span> is
          required to be a Network Card Interface name (e.g. eth0). Inside
          this file are attributes to this interface, such as its IP
          address(es), subnet masks, and so forth. It is necessary that the
          stem of the filename be <span class=
          "emphasis"><em>ifconfig</em></span>.
        </p>
        <div class="admon note">
          <img alt="[Note]" src="../images/note.png" />
          <h3>
            Note
          </h3>
          <p>
            If the procedure in the previous section was not used, Udev will
            assign network card interface names based on system physical
            characteristics such as enp2s1. If you are not sure what your
            interface name is, you can always run <span class=
            "command"><strong>ip link</strong></span> after you have booted
            your system. Again, it is important that ifconfig.xyz is named
            after correct network card interface name (e.g. ifconfig.enp2s1
            or ifconfig.eth0) or your network interface will not be
            initialized during the boot process.
          </p>
        </div>
        <p>
          The following command creates a sample file for the <span class=
          "emphasis"><em>eth0</em></span> device with a static IP address:
        </p>
        <pre class="userinput">
<kbd class="command">cd /etc/sysconfig/
cat &gt; ifconfig.eth0 &lt;&lt; "EOF"
<code class="literal">ONBOOT=yes
IFACE=eth0
SERVICE=ipv4-static
IP=192.168.1.2
GATEWAY=192.168.1.1
PREFIX=24
BROADCAST=192.168.1.255</code>
EOF</kbd>
</pre>
        <p>
          The values of these variables must be changed in every file to
          match the proper setup.
        </p>
        <p>
          If the <code class="envar">ONBOOT</code> variable is set to
          <span class="quote">&ldquo;<span class=
          "quote">yes</span>&rdquo;</span> the System V network script will
          bring up the Network Interface Card (NIC) during booting of the
          system. If set to anything but <span class=
          "quote">&ldquo;<span class="quote">yes</span>&rdquo;</span> the NIC
          will be ignored by the network script and not be automatically
          brought up. The interface can be manually started or stopped with
          the <span class="command"><strong>ifup</strong></span> and
          <span class="command"><strong>ifdown</strong></span> commands.
        </p>
        <p>
          The <code class="envar">IFACE</code> variable defines the interface
          name, for example, eth0. It is required for all network device
          configuration files.
        </p>
        <p>
          The <code class="envar">SERVICE</code> variable defines the method
          used for obtaining the IP address. The LFS-Bootscripts package has
          a modular IP assignment format, and creating additional files in
          the <code class="filename">/lib/services/</code> directory allows
          other IP assignment methods. This is commonly used for Dynamic Host
          Configuration Protocol (DHCP), which is addressed in the BLFS book.
        </p>
        <p>
          The <code class="envar">GATEWAY</code> variable should contain the
          default gateway IP address, if one is present. If not, then comment
          out the variable entirely.
        </p>
        <p>
          The <code class="envar">PREFIX</code> variable contains the number
          of bits used in the subnet. Each octet in an IP address is 8 bits.
          If the subnet's netmask is 255.255.255.0, then it is using the
          first three octets (24 bits) to specify the network number. If the
          netmask is 255.255.255.240, it would be using the first 28 bits.
          Prefixes longer than 24 bits are commonly used by DSL and
          cable-based Internet Service Providers (ISPs). In this example
          (PREFIX=24), the netmask is 255.255.255.0. Adjust the <code class=
          "envar">PREFIX</code> variable according to your specific subnet.
          If omitted, the PREFIX defaults to 24.
        </p>
        <p>
          For more information see the <span class=
          "command"><strong>ifup</strong></span> man page.
        </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <h2 class="sect2">
          <a id="resolv.conf" name="resolv.conf"></a>7.5.2. Creating the
          /etc/resolv.conf File
        </h2>
        <p>
          If the system is going to be connected to the Internet, it will
          need some means of Domain Name Service (DNS) name resolution to
          resolve Internet domain names to IP addresses, and vice versa. This
          is best achieved by placing the IP address of the DNS server,
          available from the ISP or network administrator, into <code class=
          "filename">/etc/resolv.conf</code>. Create the file by running the
          following:
        </p>
        <pre class="userinput">
<kbd class="command">cat &gt; /etc/resolv.conf &lt;&lt; "EOF"
<code class="literal"># Begin /etc/resolv.conf

domain <em class="replaceable"><code>&lt;Your Domain Name&gt;</code></em>
nameserver <em class=
"replaceable"><code>&lt;IP address of your primary nameserver&gt;</code></em>
nameserver <em class=
"replaceable"><code>&lt;IP address of your secondary nameserver&gt;</code></em>

# End /etc/resolv.conf</code>
EOF</kbd>
</pre>
        <p>
          The <code class="varname">domain</code> statement can be omitted or
          replaced with a <code class="varname">search</code> statement. See
          the man page for resolv.conf for more details.
        </p>
        <p>
          Replace <em class="replaceable"><code>&lt;IP address of the
          nameserver&gt;</code></em> with the IP address of the DNS most
          appropriate for the setup. There will often be more than one entry
          (requirements demand secondary servers for fallback capability). If
          you only need or want one DNS server, remove the second
          <span class="emphasis"><em>nameserver</em></span> line from the
          file. The IP address may also be a router on the local network.
        </p>
        <div class="admon note">
          <img alt="[Note]" src="../images/note.png" />
          <h3>
            Note
          </h3>
          <p>
            The Google Public IPv4 DNS addresses are 8.8.8.8 and 8.8.4.4.
          </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <h2 class="sect2">
          <a id="ch-scripts-hostname" name="ch-scripts-hostname"></a>7.5.3.
          Configuring the system hostname
        </h2>
        <p>
          During the boot process, the file <code class=
          "filename">/etc/hostname</code> is used for establishing the
          system's hostname.
        </p>
        <p>
          Create the <code class="filename">/etc/hostname</code> file and
          enter a hostname by running:
        </p>
        <pre class="userinput">
<kbd class="command">echo "<em class=
"replaceable"><code>&lt;lfs&gt;</code></em>" &gt; /etc/hostname</kbd>
</pre>
        <p>
          <em class="replaceable"><code>&lt;lfs&gt;</code></em> needs to be
          replaced with the name given to the computer. Do not enter the
          Fully Qualified Domain Name (FQDN) here. That information is put in
          the <code class="filename">/etc/hosts</code> file.
        </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <h2 class="sect2">
          <a id="ch-scripts-hosts" name="ch-scripts-hosts"></a>7.5.4.
          Customizing the /etc/hosts File
        </h2>
        <p>
          Decide on the IP address, fully-qualified domain name (FQDN), and
          possible aliases for use in the <code class=
          "filename">/etc/hosts</code> file. The syntax is:
        </p>
        <pre class="screen">
<code class="literal">IP_address myhost.example.org aliases</code>
</pre>
        <p>
          Unless the computer is to be visible to the Internet (i.e., there
          is a registered domain and a valid block of assigned IP
          addresses&mdash;most users do not have this), make sure that the IP
          address is in the private network IP address range. Valid ranges
          are:
        </p>
        <pre class="screen">
<code class="literal">Private Network Address Range      Normal Prefix
10.0.0.1 - 10.255.255.254           8
172.x.0.1 - 172.x.255.254           16
192.168.y.1 - 192.168.y.254         24</code>
</pre>
        <p>
          x can be any number in the range 16-31. y can be any number in the
          range 0-255.
        </p>
        <p>
          A valid private IP address could be 192.168.1.1. A valid FQDN for
          this IP could be lfs.example.org.
        </p>
        <p>
          Even if not using a network card, a valid FQDN is still required.
          This is necessary for certain programs to operate correctly.
        </p>
        <p>
          Create the <code class="filename">/etc/hosts</code> file by
          running:
        </p>
        <pre class="userinput">
<kbd class="command">cat &gt; /etc/hosts &lt;&lt; "EOF"
<code class="literal"># Begin /etc/hosts (network card version)

127.0.0.1 localhost
<em class="replaceable"><code>&lt;192.168.1.1&gt;</code></em> <em class=
"replaceable"><code>&lt;HOSTNAME.example.org&gt;</code></em> <em class=
"replaceable"><code>[alias1] [alias2 ...]</code></em>

# End /etc/hosts (network card version)</code>
EOF</kbd>
</pre>
        <p>
          The <em class="replaceable"><code>&lt;192.168.1.1&gt;</code></em>
          and <em class=
          "replaceable"><code>&lt;HOSTNAME.example.org&gt;</code></em> values
          need to be changed for specific uses or requirements (if assigned
          an IP address by a network/system administrator and the machine
          will be connected to an existing network). The optional alias
          name(s) can be omitted.
        </p>
        <p>
          If a network card is not going to be configured, create the
          <code class="filename">/etc/hosts</code> file by running:
        </p>
        <pre class="userinput">
<kbd class="command">cat &gt; /etc/hosts &lt;&lt; "EOF"
<code class="literal"># Begin /etc/hosts (no network card version)

127.0.0.1 <em class=
"replaceable"><code>&lt;HOSTNAME.example.org&gt;</code></em> <em class=
"replaceable"><code>&lt;HOSTNAME&gt;</code></em> localhost

# End /etc/hosts (no network card version)</code>
EOF</kbd>
</pre>
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